Low-noise near-infrared optical frequency comb from a femtosecond diode-pumped solid state laser

Following the demonstration of the first fully stabilized solid state laser frequency comb operating in the 1.5-µm spectral region [1,2], we present a detailed analysis of the noise properties of this comb and show its superior noise performances compared to a commercial fiber-laser comb stabilized using similar feedback electronics. Our comb is based on a ∼200-fs Er:Yb:glass laser oscillator (ERGO) generating ∼90 mW average output power, pumped by 600 mW from a 980-nm telecom-grade laser diode. The ERGO laser generates a coherent octave-spanning frequency comb in a 1.5-m long dispersion-flattened, polarization-maintaining, highly nonlinear fibre without any additional amplification. The ∼40-mW average power supercontinuum is polarized, stable, and was optimized for a strong carrier envelope offset (CEO) frequency signal. The CEO-beat, detected in a standard f-to-2f interferometer [3], is 49 dB above the noise floor in a 100-kHz resolution bandwidth and has the narrowest linewidth (3.6 kHz) of a free-running CEO achieved in the 1.5-µm spectral region. Full comb stabilization is obtained by phase-locking both the CEO and the repetition rate to the same 10-MHz local reference. Feedback is applied to a piezo-transducer controlling the cavity length to lock the repetition rate to f rep = 75 MHz and to the pump diode current to lock the CEO-beat to |f CEO |=20 MHz.